For me, it's because an iPad lets me perform tasks that a laptop either can't do, or can't do as well.
The image below best sums up why I often choose to use an iPad to do the stuff that I do, because that's the nature of my work.
For context, I am a primary school teacher using his iPad to help teach in the classroom. My main use case is notability in the classroom, mirrored to the projector via an Apple TV. Writing on documents is smooth thanks to the Apple Pencil, and the integrated nature of the Smart Keyboard allows me to switch seamlessly between typing and tablet mode. It also frees me up to move around the classroom and better monitor my students' progress.
And while consumption seems like a dirty word around here, this is also a significant part of my work as a teacher. I have my teaching material organised in notability, making it easy for me to access when I want to review them. The iPad is also a great presentation tool, and fun for note taking during meetings (in part due to the longer battery life, the lightweight form factor, and apps). Having an iPad in front of you somehow looks more "serious" compared to a smartphone, even if I have Apollo (a reddit client) opened alongside notes, with telegram in slide-over.
Other things that are possible on an iPad include scanning documents with scanner pro, using the camera to double as a visualiser, recording videos (the iPad has a great camera) to later edit using lumafusion, and when marking books, the iPad+Smart Keyboard form factor takes up less space on my desk overall compared to a laptop. I sometimes use mindnode to organise my thoughts, or Things to plan tasks, and overall, the iPad is just this right compromise of ease of use and accessibility for me.
And when I am at home, the iPad is the ultimately consumption tool.
I don't get that same fluidity with a laptop. MacBooks lack touchscreens, and windows software is still pretty clunky and not at all optimised for touch. I also have an iMac and a MBA which I use for the heavy lifting, like working on documents, and preparing lesson material. So in a sense, I am able to get by using an iPad at work because I have another PC elsewhere to fill in the gaps where the iPad can't. I am not all-in on my iPad, and that was never my goal, but I do try to push the boundaries on what can be done on my iPad from time to time.